This lithium-ion rechargeable battery contains a flat wound electrode body. A positive electrode terminal and a negative electrode terminal are connected to the wound electrode body, and arranged so that part of each terminal is projected to the outside from the lid of a battery case. Further, when the length in a winding axis direction of the wound electrode body is W, the size of the wound electrode body in the direction perpendicular to the winding axis direction and parallel to the flat surface is H, and a distance between the position farthest from the lid in a connection range in which the positive electrode terminal and/or the negative electrode terminal is connected to a non-coated portion and the edge arranged on the side of the lid portion in the wound electrode body is X, the values of W, H and X are determined so that a point defined in a plane (X/H, H/W) by values (X/H); and (H/W) is positioned in a triangular area made by connecting three points, (0.50, 0.70), (0.32, 0.40), (0.70, 0.40) in the same plane.